The present application relates generally to ice making machines, and specifically to ice harvest controls and sensors as used therein.
Ice making machines are well known in the art, and typically include an ice cube making mechanism located within a housing along with an insulated ice retaining bin for holding a volume of ice cubes produced by the ice forming mechanism. In one type of ice maker a vertically oriented evaporator plate is used to form a slab of ice characterized by a plurality of individual cubes connected by ice bridges there between. As the slab falls from the evaporator plate into the ice bin, the ice bridges have a tendency to break forming smaller slab pieces and individual cubes. As is well understood, the ice slab is formed by the circulating of water over the cooled surface of the evaporator plate, the plate forming a part of a refrigeration system including a compressor and a condenser.
Of critical importance to ice makers of this general type, is knowing when the ice is of sufficient thickness to be harvested. Once the harvest point is reached, the making of ice is discontinued by stopping the flow of water over the evaporator and the cooling thereof. The evaporator plate is then heated, typically by the use of hot gas from the refrigeration system. The ice slab then melts slightly releasing its adhesion to the plate so that it can fall into the bin positioned there below. Various controls have been proposed and used over the years to signal the harvest point. One approach is to use electrical conductivity whereby an electrical probe is positioned closely adjacent the surface of the evaporator. When ice builds to a desired thickness the plate comes in contact with the flow of water causing a conductivity connection which can trigger the harvest cycle. A problem with this sensor type concerns the evaporative or electrically caused chemical deposition on the probe resulting in a weak or no signal failure condition wherein the harvest point is not detected.
The harvest point can also be indicated by the lost water approach. In ice makers of the above described type, a water pan is positioned below the evaporator to catch the water not immediately frozen thereon. The water is then recycled from the tray back over the evaporator. If water that freezes on the evaporator is not replenished into that water circulatory system, then the water level in the pan will gradually be lowered as the ice is formed. Thus, various techniques have been used to sense the low water level point that corresponds with a desired ice build-up or thickness. It is known to use an electromechanical float mechanism that can signal when that point is reached. However, such systems are prone to mechanical failure whereby contact with the water can lead to corrosion and fouling problems. Other sensors including photo optical sensors are used, but again are located in or closely adjacent the water pan and thereby subject to corrosive or depositional effects that can degrade the performance thereof.
Accordingly, it would be desirable to have an ice harvest sensing system that is significantly less likely to be damaged or subject to corrosive or depositional effects and can thereby accurately and reproducibly sense, over time, the proper harvest point.
The present invention comprises an ice harvest system for use in an ice maker. The ice maker herein works in the conventional manner wherein a refrigeration system provides for cooling of the evaporator. Ice is formed thereon as water is pumped by a re-circulating pump to flow from a water distribution tube over the evaporator surface. Water that is not frozen thereon flows into a water pan positioned there below. A pressure fitting is positioned in the pan at the bottom thereof and connected to a pneumatic tube. The pneumatic tube is connected to a pressure sensor located on a control board at a position remote from the water pan. As water fills the pan it attempts to flow into the fitting interior. Air trapped in the fitting and in the tube is compressed slightly by this action and this pressure is communicated through the tube to the pressure transducer/sensor. The sensor then converts this pressure into a voltage reading, which is input to and converted by a microprocessor of the control board for interpretation as a pressure value. As the water level in the tray lowers, the pressure transmitted to the pressure sensor reduces. When a predetermined low pressure is sensed, a harvest point is reached and a harvest cycle is initiated. In particular, the water pump is stopped along with cooling of the evaporator. A hot gas valve is then opened to warm the evaporator resulting in the discharge of the ice there from.
A major advantage of the pressure sensing strategy of the present invention is the location of the pressure sensor on the control board at a point within the ice maker substantially distant from the water tray. As a result thereof, any water based degradation thereof due to sedimentation, corrosion or the like is greatly minimized, if not eliminated. The control of the present invention is also low in cost as the tube and pressure fitting are inexpensive and easily replaced and as the pressure sensor is relatively inexpensive relative to other sensor/transducer technologies.